1. Field of the Invention
The invention relates to data backup in virtual volumes managed by a storage controller.
2. Description of the Related Art
A capacity expansion technique is known (for example, JP-A-2003-15915 (Patent Document 1)). In the capacity expansion technique, when write is generated with respect to a certain virtual area in a virtual volume, an unallocated actual area in a pool is allocated to the virtual area of a write destination, and a data element as a write target is written in the actual area.
Data in logical volumes can be backed up by each volume. In the case that data in virtual volumes are backed up by each volume, reading is generated with respect to all virtual areas, therefore, reading is generated also with respect to virtual areas to which actual areas are not allocated. That is unnecessary reading.
In addition, meaningless data elements (for example, null data elements) obtained by the reading are also backed up with significant data elements (data elements read from actual areas allocated to the virtual volume). Accordingly, meaningless data elements are stored in a backup destination, therefore, the storage capacity is consumed uselessly.
Furthermore, in restore of data in the virtual volume, not only significant data elements but also the meaningless data elements are restored, therefore, actual areas are allocated to all virtual areas included in the restored virtual volume. As a result, actual areas will be consumed more than actual areas allocated to the virtual volume at the time of backup, in addition, longer time is necessary for restore.
In view of the above problems, for example, a technique disclosed in JP-A-2008-181271 (Patent Document 2) has been devised.    Patent Document 1: JP-A-2003-15915    Patent Document 2: JP-A-2008-181271